a(0)=1, a(1)=3, a(2)=7; thereafter a(n) = a(n-1) + a(n-2) + 1.

Terms

a(0) =1a(1) =3a(2) =7a(3) =11a(4) =19a(5) =31a(6) =51a(7) =83a(8) =135a(9) =219a(10) =355a(11) =575a(12) =931a(13) =1507a(14) =2439a(15) =3947a(16) =6387a(17) =10335a(18) =16723a(19) =27059a(20) =43783a(21) =70843a(22) =114627a(23) =185471a(24) =300099a(25) =485571a(26) =785671a(27) =1271243a(28) =2056915a(29) =3328159